Wireless communications systems, such as cellular communications systems, are increasingly being designed and deployed in and around buildings and other architectural structures. Walls and other barriers within these architectural structures affect the ability to communicate using electromagnetic waves. In other words, electromagnetic waves may be partially or fully reflected or absorbed by a wall which may thereby inhibit transfer of information between two locations in the structure. Typically, in cellular systems, a number of base stations are distributed throughout the structure to facilitate wireless communications. The structure is divided up into regions, called cells, and generally, a base station is allocated to each cell. Hence, when a transmitter communicates with a receiver in the structure, both the transmitter and receiver communicate directly to the nearest base station.
In order to determine where base stations should be located within the structure, a signal power level meter is usually carried throughout the building and actual signal power level measurements are taken between specified locations throughout the structure. Typically, cellular communications systems are over-engineered to include more cells and base stations than are necessary so as to ensure adequate wireless communications uniformly throughout the structure. It is currently estimated that over-engineering wastes approximately $10,000 to $500,000 per cellular installation. Accordingly, it would be extremely desirable to determine wireless communications transfer characteristics between selectable locations in structures, prior to installation of cellular communications systems.
It is generally known in the art that, prior to installation of a cellular communications system, a ray tracing method may be utilized for determining a transfer function H(f) which characterizes the wireless communications channel between a transmitter location and a receiver location in a structure. The transfer function H(f) is a mathematical complex-valued function in the frequency domain, which provides the frequency domain characterization of the radio propagation channel in much the same manner that a filter is characterized by its transfer function. The transfer function H(f) provides the only complete characterization of the communications channel between two points and, as such, is of unique value relative to communication performance assessment and simulation.
The ray tracing method is a brute force method of propagation analysis with a long history. It has been used in a variety of forms for the tracing of rays in ionospheric propagation, tropospheric propagation, and in the analysis of numerous other physical propagation channels. Until the advent of powerful computers that characterized the 1990s, however, the major drawback to ray tracing has always been the limitations of computer power and computation time. Currently, there has been a resurgence of interest in ray tracing, especially in the art of computer graphics.
The ray tracing method involves searching for communications channels between a transmitter location and a receiver location. In general, rays are graphically projected in all directions from the transmitter location in an artificially created computer space, tracing each ray as it encounters walls and other obstacles, while applying the wall properties (reflection and transmission coefficients) to the transmitted and reflected rays, and finally determining if the ray passes close enough to the receiver to be counted as a ray that is supported by the communications channel. The majority of the rays are usually discarded.
Although the ray tracing method can be used to accurately determine wireless communications transfer characteristics, this method requires numerous and complex computations, which get more pronounced as room geometries get more complicated and the number of rooms increases. Furthermore, the requisite numerous computations result in slow operation and the inability to construct a portable real-time tool for determining wireless communications transfer characteristics. Finally, there is no way of checking, or validating, results which are generated by using the ray tracing method.